Method of explosive pulverization



` July `17, 1951 w. E. LOBO 2,560,807

METHOD OF EXPLOSIVE PULVERIZTI-ON Filed Sept. 18, 1947 /ls as INVENTOR WALTER E. LOBO ATTORNEYS I in external pressure.

Patented July 17, 1951 METHOD OF EXPLOSIVE PULVERIZATION Walter E. Lobo, Westfield, N. J., assignor to The M. W. Kellogg Co., Jersey City, N. J., a corporation of Delaware Application September 18, 1947, Serial No. 774,768

4 claims. I

This invention relates to an improved method for reducing coal to finely powdered form and more particularly to a continuous flow explosion pulverization method in which coal is slurried with water and pumped as a slurry to an elevated pressure preliminary to explosion pulverization, after which high-pressure steam is employed as the explosion pulverization medium and is recompressed without condensation after explosion pulverization for reuse.

Finely powdered coal has recently become of greatly increased importance because of its proposed use in combustion turbines as well as in the development of new fuels comprised of oil with nely powdered coal colloidally suspended therein. It has,.therefore, been proposed that some method of finely powdering the coal at less cost than grinding be found. It is an object of the present invention to provide such a method and it is proposed to explosively pulverize the 4into the hopper the explosion pulverization medium to a desired elevated pressure. After the proper pressure was attained and the explosion pulverization medium had permeated the particles of the material, the pressure was suddenly released either by opening the hopper or by passing the material through an expansion nozzle so that, the explosion pulverization medium within the interstices of each particle tended to fracture its structure and divide it because of the pressure differential created by the sudden reduction It is an obpject of the present invention to provide an explosion pulverization process in which the material in coarse form may be pumped to the elevated pressure in slurry form prior to explosion pulverization.

Although the process may be employed to pulverize materials other than coal or in connection with explosion pulverization mediums other than water or steam, it will be described in connection with the preferred process for the pulverization of bituminous coal using water as a slurrying medium and steam as all or a part of the explosion pulverization medium.

In the drawing, coarse coal Ill is withdrawn from a supply hopper I I through a suitable means such as a standpipe I2 to be formed into a slurry in line I3 with water supplied under low pressure suitable yfor slurrying by pump I4. The slurry thus formed is pumped to an elevated pressure suitable for explosion pulverization by highpressure pump I5 which delivers its high-pressure slurry through line IB to tank I1. which in the preferred form of my invention isa separator for separating the slurry water from the coarse coal. According to this preferred method, slurrying water is recycled for reuse in the slurrying step through pipe I8, pipe I9, low-pressure pump 2u on pipe 2 I. The coarse coal is fed from the lower portion of separator tank I1 through outlet 22 to high-pressure steam line 23 where the coarse material under high pressure is entrained in the rapidly flowing steam and carried to a suitable means for suddenly reducing the pressure, such as an explosion pulverization nozzle 25 which is illustrated as projecting the high pressure steam and entrained coarse particles against a bale 26 within a low-pressure tank 21.

The low-pressure steam from tank 21 is withdrawn overhead through line 28 and passed through a separator 29 in order to eliminate any particles remaining entrained, and is then diverted through line 30 to compressor 3I and, if necessary, or preferable, through a heater 32, to be recycled to the high-pressure line 23 through line 33.

The partially pulverized coal produced in tank 21 by the explosive reduction in pressure in nozzle 25 is withdrawn through line 34 and, after being united with the particles separated in separator 29 is screened by screen 35 which permits the product powder to pass into outlet pipe 36 While the oversized particles are carried preferably by water through line 31 into line I9 to be reintroduced into the slurry and recycled through high-pressure pump I5 and the explosion pulverization step.

In some cases it will be found practicable to retain some of the slurry water with the coarse material so that it flows from outlet 22 in the form of a dense slurry. In other cases it may be possible to eliminate tank I1 entirely and to pump the slurry directly from pump I5 to explosion pulverization means 25, preferably introducing high-pressure steam through line 33 or heating the slurry by any other suitable heating means so that when the slurry experiences a sudden reduction in pressure upon its immergence into tank 21, its water content is substantially completely vaporized; in other cases. it

is' preferred that this vaporization be only partial so that the coal particles falling to the bottom of tank 21 will remain suiliciently slurried to move through outlet v34 to the screened step at 35. Y

The invention is, of course, not limited to the details of the particular embodiment shown. For instance, any suitable means for suddenly reducing the pressure may be used in the explosion pulverization step; explosion pulverization nozzle is the preferred form. Although the process might be employed without using water, it has been found that water is uniquely adapted to the process when applied to the explosion pulverization of coal; it is not reactive with coal and is readily separable therefrom by conventional drying means.

It will be noted that the low-pressure steam withdrawn from tank 21 through overhead outlet- 28 isnot liqueiied but is recompressed for the purpose of saving the latent heat of vaporization. In a simplied form of the invention, the steam withdrawn from line 28 may be condensed, pumped up to explosion pulverization pressure, and revaporized, thus replacing compressor 3| by a condensate pump. The relative merits of recompression of the steam vs. condensation and revaporlzation can only be determined by a study of the quantities of steam used, its heat content at high and low pressures, construction costs; the relative costs of fuel and power and other factors involved in the construction particular plant.

I claim:

1. A method of pulverizing coal which includes -the steps of: reducing said coal to granular form;

`:forming a slurry of said granular coal with water;

pumping said slurry to an elevated pressure;

and operation of a Aas separating the greater portion of said water from said slurry at elevated pressure; mixing said granular material at elevated pressure with high pressure steam; suddenlyreducing the pressure on said mixture to produce explosion pulverization therein; recompressing the steam produced from said pressure reduction and recycling it to be reused in said explosion pulverization step;

screening said particles produced in said pulverization step; and recycling the oversized particles with water to said pumping step. Y

2. A combination as described in claim 1 in -which the steam produced by said explosion step is heated afterbeing recompressed.

3. A combination as described in claim 1 in which the water produced by said explosion is employed as at least a portion of the water used to slurry said granular coal.

4. A method of pulverizing a permeable frangible material by explosion pulverization with a condensable medium, which method includes the steps of: reducing said material to granular form, forming a slurry of said granular material with explosion pulverization medium in liquid form; pumping said slurry to an elevated pressure; separating the greater portion of said liquid from said slurry at elevated pressure; mixing the remaining slurry at elevated pressure with said medium in the form of a heated vapor; suddenly reducing the pressure on said mixture to produce explosion pulverization therein; recompressing the vapor remaining after said pressure reduction and recycling it to be reheated and reused in said explosion pulverization step; screening the solid particles produced by said explosion pulverization step; and recycling the over-sized particles and remaining liquid to said pumping step. l I

WALTER E. LOBO.

REFERENCES CITED The following references are of record in the le of this patent:

,UNITED STATES PATENTS OTHER REFERENCES Chem. & Met. Eng., February 1941, pgs. 122-125. (Copy in Scientiiic Library.) 

1. A METHOD OF PULVERIZING COAL WHICH INCLUDES THE STEPS OF: REDUCING SAID COAL TO GRANULAR FORM; FORMING A SLURRY OF SAID GRANULAR COAL WITH WATER; PUMPING SAID SLURRY TO AN ELEVATED PRESSURE; SEPARATING THE GREATER PORTION OF SAID WATER FROM SAID SLURRY AT ELEVATED PRESSURE; MIXING SAID GRANULAR MATERIAL AT ELEVATED PRESSURE WITH HIGH PRESSURE STEAM; SUDDENLY REDUCING THE PRESSURE ON SAID MIXTURE TO PRODUCE EXPLOSION PULVERIZATION THEREIN; RECOMPRESSING THE STEAM PRODUCED FROM SAID PRESSURE REDUCTION AND RECYCLING IT TO BE REUSED IN SAID EXPLOSION PULVERIZATION STEP; SCREENING SAID PARTICLES PRODUCED IN SAID PULVER- 